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Hurricane study whips up a storm

By Catherine Brahic and Reuters

(Image: stock.xchng)

Rising ocean temperatures linked to global warming could decrease the number of hurricanes hitting the United States, say researchers. But their findings have been questioned by some at a recent meteorology conference.

The new study challenges research suggesting that global warming could be contributing to an increase in the frequency and the intensity of Atlantic hurricanes. Hurricanes feed on warm water, leading to conventional wisdom supported by recent research that global warming could be revving up more powerful storms.

Chunzai Wang of the US National Oceanic and Atmospheric Administration and Sang-Ki Lee of the University of Miami, US, examined 150 years of hurricane records and found a small decline in hurricanes making landfall in the United States as oceans warmed.

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Wang says the number of those hurricanes actually hitting the United States is a much better indicator than the total number of hurricanes. This is because prior to the mid-1960s, when the advent of satellites and other technology made it easier to spot cyclones, some tropical storms and hurricanes lived and died far out at sea, undetected.

‘Clear link’

“The attribution of the recent increase in Atlantic hurricane activity to global warming is premature,” say the researchers. “Global warming may decrease the likelihood of hurricanes making landfall in the United States.”

Mark Saunders of Tropical Storm Risk at the University College of London, UK, disagrees with Wang and Lee’s assessment that landfall is a more accurate indicator of the long-term trends in hurricane numbers.

“When you average over the long-term, there is a clear link between the number of hurricanes that form at sea and those that hit US,” he told New Scientist.

Lively debate

The new study suggests a link between global warming and increasing vertical wind shear, a measure of the difference in wind speeds at different altitudes. By breaking up their vertical structure, wind shear can tear apart nascent cyclones.

Wang and Lee found that warming of the tropical Pacific and Indian oceans increases Atlantic wind shear, while rising sea temperatures in the tropical North Atlantic decrease shear. The two effects compete, but according to Wang, “the Pacific and Indian warming wins and the result is a decrease in landfalling US hurricanes.”

The study triggered lively debate that the annual meeting of the American Meteorological Society, which took place in New Orleans, Louisiana, US, this week.

Richard Spinrad, NOAA’s assistant administrator for Oceanic and Atmospheric Research, called the study “seminal”, but Greg Holland, a senior scientist at the US National Center for Atmospheric Research, said it was anything but seminal.

“The results of the study just don’t hold together,” says Holland adding that other factors outweigh wind shear in determining whether or not a storm forms.